Vitamins D & K2 (MK-7)

Becky
Jul 23
5 min read

Updated: Oct 3

Vitamin D – The Sunshine Vitamin

Vitamin D is one of the most crucial vitamins for overall health, particularly for maintaining strong bones, supporting immunity, and enhancing energy levels.

Known as the "sunshine vitamin," your body can make vitamin D when your skin is exposed to sunlight — but many people still struggle with low levels, especially in winter months or if they spend most of their time indoors.

Why Vitamin D Is Important

Having good levels of vitamin D has been linked to health benefits in conditions such as cancer, heart disease, and autoimmune and allergic disorders.

• Bone Strength – Vitamin D helps your body absorb calcium, which is crucial for healthy bones and teeth.

• Immune Support – Supports the immune system, helping fight infections.

• Mood & Energy – Low vitamin D is linked to fatigue and low mood, especially in the winter.

• Muscle Health – Prevents muscle weakness and supports overall mobility.

Vitamin D helps your body absorb calcium, but vitamin K2 (particularly the MK-7 form) ensures that calcium is sent to the bones and teeth — and not to soft tissues like arteries or joints.

Why do you need both D and K2 together?

D3 increases calcium absorption.

K2 (MK-7) activates proteins that direct calcium into bones and away from blood vessels, supporting heart and bone health.

Without K2, high vitamin D intake may lead to calcium build-up in arteries (calcification).

Recommended Daily Intake (RDI)

Vitamin D (adults):

600 IU (15 mcg) – though many experts suggest 1000–4000 IU/day in winter.

Vitamin K2 (adults):

No official RDI, but 90–120 mcg/day (MK-7 form) is commonly recommended for bone and heart health.

Signs of Vitamin D Deficiency

The Endocrine Society defines vitamin D insufficiency as 25(OH)D below 30 ng/mL (73 nmol/L). Check carefully which units of measurement your test uses, as this makes a significant difference.

Signs of deficiency include:

• Fatigue or low energy

• Low mood or depression (especially winter blues)

• Frequent infections or slow healing

• Bone pain or frequent fractures

• Weak muscles or cramps

Top Sources of Vitamin D

There are two forms of vitamin D: vitamin D2 and vitamin D3.

Vitamin D3 is the form that our skin makes from cholesterol when it is exposed to UVB rays from the sun, and is then activated in our liver into the form calcidiol (25(OH)D).

Sunlight is the best source of vitamin D; however, many of us do not get enough sun exposure due to our indoor lifestyle, clothing and the use of sunscreens with high sun protection factors.

It is estimated that daily sunshine for 7–30 minutes is required to meet the vitamin D dose.

Sunshine is best at midday. You get the least vitamin D from the sun when you are well-clothed and standing up; you get the most D from the sun when you are wearing minimal clothes and are lying down. The darker or older your skin, the more time you need in the sun, or the more you should focus on exposing more skin and lying down.

In the UK, the sun is only high enough to activate vitamin D between April and October each year (The UVB wavelengths need to be in the range 290-315 nm). Therefore, the government recommends that everyone supplement their vitamin D intake between November and March, or throughout the year if they cannot get sufficient sun exposure on their skin.

You can estimate how much vitamin D your sun exposure gives you with the "D Minder" app.

Food sources of vitamin D:

Salmon (wild): 100 g = 600–1000 IU D3

Sardines: 100 g = 270 IU D3

Egg yolks: 1 egg = 40 IU D3

Mushrooms: Depends on UVB exposure D2.

Fortified foods (milk, yogurt, plant milks): 100–200 IU per serving

Cod liver oil: 1 tsp = 450 IU D3

Top Food Sources of Vitamin K2 (MK-7)

Natto (fermented soybeans): 1 tbsp = 100 mcg

Hard cheeses: 30 g = 20–30 mcg

Goose liver: 100 g = 30–40 mcg

Egg yolks: 1 egg = 5–8 mcg

Chicken (dark meat): 100 g = 6 mcg

Do You Need Supplements?

People who may be at risk of Vitamin D deficiency include:

Everyone in the UK between November and March each year.
The elderly, especially if frail/house-boundPeople with dark skin (African, African-Caribbean and South Asian ethnicities).
People who are very overweight (obese) or have had gastric bypass surgeries.
Pregnant women and women who are breastfeeding.
Anyone who may spend very little time outdoors.
People with certain conditions, such as liver disease, kidney disease or cystic fibrosis (CF).
People with malabsorption conditions, e.g. Coeliac's disease or Crohn's disease.
People who have already been diagnosed with bone disease, such as osteoporosis, osteomalacia or Paget's disease.

Always check your vitamin D blood levels (25(OH)D test) before taking high doses of vitamin D.

Most people should aim for their vitamin D status to be 30-40 ng/mL (75-100 nmol/L)

The Endocrine Society recommends a dose of 600–2000 IU per day (depending on the amount of sunlight you are exposed to).

The European Food Safety Agency and the IOM determined that the upper tolerable limit of vitamin D intake in adults is 4000 IU/day (100 µg/day).

If you supplement with vitamin D, it is crucial to choose one that includes vitamin K2 (MK-7) to support your bones and ensure you are getting enough calcium in your diet.

Note that vitamin D supplements must be taken with fat to be effectively absorbed.

Vitamin D3 Supplements have been well studied to effectively raise 25(OH)D levels, and the great news is that they are now available for vegans (paid link).

Vegan Vitamin D3 2000iu & K2 Liquid drops

We use this Vitamin D3 4000 iu & Vitamin K2 MK7 100μg from Amazon (paid link)

Vitamin D3 4000 iu & Vitamin K2 MK7 100μg

When Elliot was bedridden, he was not able to tolerate vitamin D supplements, and so we used a CareLamp UVB-NARROWBAND PHOTOTHERAPY LAMP on his skin (waveband emission 305-315 nm).

Sperti also makes a Vitamin D light, which provides natural vitamin D from UVB light throughout the year.

Vitamin D2 supplements are available; however, I would not recommend taking them, as a recent meta-analysis of data has shown that supplementing with vitamin D2 can actually reduce your serum 25(OH)D levels (see link below).